Radio transmitting system



Dec. 18, 1934 B COLEMAN 1,985,019

RADIO TRANSMITTING SYSTEM Filed May 11, 1927 nun nun

WITNESSES: INVENTOR /Z J, 7W John B. C a/emar) ATTORNEY Patented Dec. 18, 1934 RADIO TRANSMITTING SYSTEM John B. Coleman, Edgewood, Pa., assignor Westinghouse Electric & Manufacturing Co pany, a corporation of Pennsylvania Application May 11, 1927, Serial No. 190,543

6 Claims.

My invention relates to radio transmitting systems, and it has particular relation to methods and instrumentalities whereby a signal may be superimposed upon the output of a radiofrequency oscillation generator.

One object of my invention is to provide means whereby the output of high-powered thermionic oscillation-generators may be interrupted at signal frequency.

Another object of my invention is to provide means whereby the keying of high-powered oscillation generators may be accomplished at extremely high speeds.

Another object of my invention is to provide means whereby the keying of high-powered oscillation generators may be accomplished without subjecting the keying device to destructive currents.

Still another and more specific object of my invention is to provide means whereby thermionic devices may be substituted for mechanically actuated relays in radio transmitting systems in which keying is accomplished by varying the grid-bias on one or more of the thermionic devices comprised in the said system,

Substantially all high-powered radio transmitting systems in use at present comprise a plurality of thermionic devices so arranged as to function either as master-oscillators, poweramplifiers, modulators, or oscillation generators. When being utilized for telegraphy, the output of such systems must be interrupted, or changed either in amplitude or frequency, corresponding in the art as keying.

Numerous keying systems have been proposed in the past, among which may be mentioned the direct control of the master oscillator either as to frequency or state of oscillation, absorption of the output of the entire system in a dummy antenna, and the interruption of the generated oscillations by an alteration of the grid bias on one or more of thermionic devices comprised in the power amplifier, or master-oscillator stages. A system of the latter type is illustrated and described in the patent to C01- pitts, 1,198,700, and it is with analagous systems that the present invention is concerned.

When it is desired to control a high-powered transmitter at high speeds, by impressing a sufiiciently high negative bias on the grids of certain of the thermionic devices comprising the power-amplifier, it is difiicult to construct a. key-responsive, high speed relay that is sufliciently light to operate at the desired speeds and safely carry the large gridto which it must be high.

I have, therefore,

subjected may be extremely by the present invention,

dispensed with relays for handling heavy gridcurrents, and have substituted therefor a pludevices arranged in cascade,

the first tube in the series, which may be of lower power than t direct control of a he others, being under the high-speed relay, and the last tube of the series being utilized to vary the grid bias on the tube to be controlled.

Among the novel features of my invention are those particularly set claims.

embodiment thereof,

taken in connection with the accompanying drawing.

The single figure of the drawing is a diagrammatic view illustrating the application of a preferred form of amplifier stage of trolled radio transm my invention to the powera piezo-electric crystal conitting system.

Referring specifically to the drawing, a crystalcontrolled master-oscillator comprises a thermionic device 1 havi ng an input circuit in which is connected a piezo-electric crystal 2 shunted by a resistor 3 and having an output nected a source of 5 and an inductor denser 7. The filam 1 may be energized trated, or both the B-battery 5 may be tors.

The and the condenser 7 quency, which may a C-battery 4 in series, and

circuit in which is serially conplate potential, or B battery 6 shunted by a tuning conent of the thermionic device from a battery 8, as illusfilament battery and the replaced by suitable generaoutput circuit comprising the inductor 6 is tuned to the desired frebe that of the piezo-electric crystal or may be a harmonic thereof.

A power amplifier stage comprises a thermionic device 11 havin is serially included a tuning condenser potential.

g an output circuit in which an inductor 12 shunted by The filament of the thermionic device is energized from a potential source 17 and this source, as well as the source 14 of anode potential, may be replaced by suitable generators, if desirable.

The cathodes of both the master oscillator tube and the power amplifier tube are provided with ground connections 18 and 21 respectively.

A radio frequency choke coil 22 is connected at one end to the grid of the power amplifier tube and at the other end through a conductor 23 to the output circuit of a thermionic device which will later be described.

A condenser 24 is interposed, between the output circuit of the master oscillator tube 1 and the input circuit of the tube 11, which condenser, together with the choke coil 22 and the common ground-connections 18 and 21 provides the necessary coupling between the two tubes.

Referring now specifically to the lower portion of the drawing, the keying portion of my system comprises a thermionic device 25 having a filament 26, a grid 27 and a plate 28. The grid is connected to the front and back contacts 31 and 32, of a high speed relay 33, having an armature 34 and the winding of the relay is connected in series with a battery 35 and a telegraph key 36. An additional front contact 37 and an additional back contact 38 are associated with the movable armature 34 of the high speed relay. The front contact 37 is connected to a point toward the negative end of a potentiometer 41 which is arranged in shunt to a grid biasing battery 42, while the back contact 38 is connected to a point near the positive end of the same potentiometer.

The positive pole of the battery 42 is conductively connected to the cathode 26. A source 423, which preferably is a battery, supplies filament power for the thermionic device and a resistor 44 in series with a source 45 of plate potential constitutes the output circuit thereof.

A conductive connection 46 extends from a point intermediate one end of the resistor 44 and the negative pole of the B-battery 45 to the grid 47 of a thermionic device 48 which device also is provided with a filament 51 and a plate 52. The thermionic device 48 is preferably of much higher power than the device 25 associated with the high speed relay 33. The output of plate circuit of the thermionic device 48 comprises a resistor 53 and a source 54 of plate potential.

Inasmuch as a conductor 55 which is common to the cathodes of both the thermionic devices 25 and 48 is provided with a ground connection 56, the resistor 53 included in the output circuit of the thermionic device 48 also is effectively included in the input circuit of the power amplifier device 11. This resistor is shunted by a condenser 57, which condenser provides a path for radio frequency currents.

In order to explain the operation of my system, it is first assumed that the master oscillator stage has been energized and is exciting the grid circuit of the power amplifier stage at the proper frequency. The power amplifier stage will deiiver to the output conductors an amplified reproduction of the input voltage variations, provided the bias on the grid thereof is of such value that space current can flow therein. The value of the grid bias depends upon the potential of the conductor 23 with respect to ground, as determined by the resistance drop in the resistor 53.

When the telegraph key 36 is moved to the up or open position, the movable armature, by establishing a circuit between the front contacts 31 and 37, impresses a high negative bias on the grid of the thermionic device 25 with respect to the filament 26. This high negative bias causes the plate current in the said device to diminish and consequently the IR, or resistance, drop across the resistor is less than it Was before the key was opened. This lessening of the IR drop causes, in turn, the grid of the thermionic device 48 to become more positive than it was thus permitting a larger plate current to flow therein. The increased plate current results in an increase of the IR drop across the resistor 53 and as a consequence the grid of the power amplifier becomes more negative.

The constants of the circuit including the control tubes 25 and 48 are so adjusted and proportioned that when the key is in its up position the IR drop in the resistor 53 is sufiicient to cause complete or substantially complete stoppage of plate current in the power amplifier tube 11.

When the telegraph key 36 is in the down or closed position, the movable armature of the relay moves to establish a circuit between the back contacts 32 and 38 and permits a potential, less negative with respect to the cathode, to be placed upon the grid of the first control tube 25. A current accordingly flows in the plate circuit thereof, which causes a resistance or IR drop in the resistor 44, thus making the end thereof, which is connected to the grid 47 of the second control tube 48, negative with respect to the cathode thereof. The plate current in the second control tube 48 is accordingly diminished from the value it had previous to the depression of the telegraph key, and the lessening of resistance or IR drop in the resistor 53 accordingly causes the conductor 23 to assume a less negative bias with respect to the cathode 51 than it had previously. Inasmuch as the cathodes of the second control tube 48 and the power ampli fier tube 11 are connected together through ground, the grid of the power amplifier tube 11 accordingly assumes substantially the same potential, with respect to its cathode as that of the conductor 23 with respect to the cathode 51. The grid of the power amplifier tube now being less negative with respect to the cathode thereof than it was previous to the depression of the telegraph key, accordingly permits the flow of plate current therein and the consequent impressing upon the output circuit thereof of an amplified copy of the input excitation frequency from the master oscillator.

The system therefore is in the nature of a grid-bias amplifier. When the telegraph key is down, oscillations will be transferred from the power amplifier to the next stage or to an antenna. When the key is up, the power amplifier is biased to the "cut off point and accordingly does not amplify the oscillations impressed thereon from the master oscillator stage.

It is apparent that the relay 33 may be extremely light in construction, inasmuch as it is required to handle only a very small amount of power. The voltage of the grid-biasing source 42 need not be high, since this tube may be of 13116 ordinary power-amplifier type, such as is used in radio receiving apparatus. This second control tube 48 may be a five-watt transmitting tube and, if desirable, a third or fourth stage may be introduced, each. stage utilizing, thermionic derelay, grid biasing battery, and chosen merely as illustrative, other analogous devices being, as will be understood by those skilled in the art, easily substituted therefor.

It is also feasible to apply my improved keying arrangement to any other tube or series of tubes comprised in a radio transmitter. In other words, it is feasible, though not particularly practical, to apply my invention to systems of the type in which no master oscillator and power amplifier are used, but in which the output of an oscillation generator is directly modulated or interrupted.

The principal advantage of my invention lies in the fact that by its use the output of a radio transmitting system of practically any desired power can be controlled at extremely high speeds by means of a very simple relay device. The contacts of the device, since they carry but a very small amount of current, need not be heavy nor is it necessary to provide the relay with excessive insulation.

Although I have illustrated and described only one specific modification of which my invention is capable, it will be obvious to those skilled in the art that many changes may be made therein. My invention, therefore, is not to be limited except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In a radio transmitting system including a master-oscillator coupled to a power amplifier comprising a thermionic device, means including a resistance coupled amplifier for varying the grid direct-current bias on said thermionic device, a resistor in the output circuit of said amplifier, said resistor being included in the input circuit of said thermionic device, and means for impressing signal frequencies on said amplifier.

2. In a communication system, an amplifier,

impressing radio-frequency current thereon, means also coupled thereto, including a resistance-coupled amplifier, for modulating said radio-frequency current, a

resistor in the output circuit of said resistanceof said first mentioned amplifier and constituting the coupling means.

3. In a communication varying circuit circuit the potential across said grid-filament said plate-filament 5. In a system for high speed transmission of signals the combination of a power tube, a master oscillator therefor, and means for stopping oscillations of said power tube, said means consisting of a vacuum tube having grid-filament power tube when current flows in said plate filament circuit, said means consisting of a resistance in said plate-filament circuit connected between the source of power for said plate and the filament of said vacuum tube and a tap connecting said resistance with the grid of said power tube, at such a point as to produce the above-mentioned grid bias.

6. In a system for high speed transmission of signals, the combination of a ter oscillator therefor, and means for the oscillations consisting 01' a vacuum tube having grid-filament and plate-filament circuits, means for varying the potential across said grid-filament circuit, said means consisting of a resistance one terminal of which is connected to the filament of said vacuum tube, means for applying alternative potentials to the other terminal of said and means within the plate-filament circuit of said vacuum tube for impressing a negative bias upon the grid of said power tube when current J OHN B. COLEMAN. 

